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⚛️ NEET Physics❓ Question

Bhai, if I sit in a moving train am I at rest or in motion? And what is average speed vs velocity actually?

Yash Tiwari11th Sample

26 Sept 2026 · 1 min read

Honestly I was a backbencher and never asked basic things. Now I'm trying to make my base proper. Motion in a Straight Line, first topic, rest and motion.

NCERT says "rest and motion are relative". But my teacher also said "Earth is moving". So when I sit in a train, I am at rest relative to the train, moving relative to the platform, and the platform is moving with Earth, which goes around the Sun, which also moves... so is anything ever actually at rest? What is the point of the idea then?

Second thing, from a MCQ: a particle goes once around a circle of radius RR in time TT. Then they asked displacement, average velocity and average speed for one full revolution. I said "average velocity = average speed = 2πR/T2\pi R/T" because "speed and velocity are the same thing in magnitude". Marked wrong. Answer was 0, 0 and 2πR/T2\pi R/T.

Why is that? Is average speed not just the magnitude of average velocity? Please explain properly bhai, I really want to fix the foundation 🙏

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  • [+]Aman YadavDropperSample· 23d ago

    There is no absolute rest. You pick a frame of reference and measure everything with respect to it. For problems on the ground we pick the ground (Earth) as the frame. That is enough.

    Average speed = total distance / total time. Average velocity = displacement / total time. After one full circle you are back where you started: displacement 0. Distance =2πR=2\pi R. That's it.

  • [+]Farhan ShaikhDropperSample· 23d ago

    Average speed is the magnitude of average velocity, so in your example both are 2πR/T2\pi R/T. The question must have been wrong.

    • [+]Arjun Nair12thSample· 23d ago

      No, Farhan, that is not generally true. The magnitude of instantaneous velocity equals instantaneous speed. For average quantities, ∣avg velocity∣=∣Δr⃗∣/Δt|\text{avg velocity}| = |\Delta \vec{r}|/\Delta t uses displacement, while average speed uses total path length. They are equal only if the motion is in a straight line without turning back. A full circle is the extreme case: displacement 0, path 2πR2\pi R. So the key was right. Average speed is always ≥∣average velocity∣\ge |\text{average velocity}|.

      • [+]Farhan ShaikhDropperSample· 23d ago

        Got it, I had mixed the instantaneous and average. Thanks Arjun.

      • [+]Yash Tiwari11thSample· 23d agoAuthor

        Haan bhai, "average" means different things for speed and velocity. Samajh gaya. Thanks Arjun bhaiya, Farhan bhai and Aman bhai.

  • [+]Siddharth RaoDropperSample· 23d ago

    Yash, the point of "relative" is that physics laws work the same in any frame that isn't accelerating (inertial frames), so we're free to choose the simplest one. A train moving at constant velocity on a straight track is as good a frame as the ground for Newton's laws.

    Also whatever frame you pick, you must treat a body as a point object when its size is tiny compared with the distances it covers. A train going 500 km is a point on the map. Same train inside the station is not a point. NCERT mentions this idea, and it shows up in short statement questions.

  • [+]Kavya NaikDropperSample· 23d ago

    Small trick for exam: whenever they say "returns to starting point", displacement and average velocity both become zero. Also for "path length between A and B along semicircle" you need to know they want distance vs displacement (πR\pi R vs 2R2R). I made a mini table of 5 of such situations and that took care of this whole section.

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